1. Field of the Invention
The present invention relates to digital broadcast receiving apparatuses and digital broadcast receiving methods and may be suitable for application to a digital broadcast receiving apparatus which receives HD (Hybrid Digital) radio using the “In Band On Channel” (IBOC) terrestrial digital radio broadcasting format, for example.
2. Description of the Related Art
In recent years, the practical use of HD radio in the IBOC terrestrial digital radio broadcasting format has increased in the United States of America. An HD radio receiver supporting HD radio is capable of receiving a simple data broadcast signal, such as traffic information and weather forecast simultaneously with a digital audio broadcast signal. More specifically, an HD radio receiver has two tuners, and the tuners are assigned for receiving a digital audio broadcast signal and for receiving a data broadcast signal, respectively.
In HD radio, the content of data sets transmitted repeatedly and continuously by data broadcast signals, is updated about every 15 minutes, and the data sets having the same content are repeatedly transmitted until updated. For example, as illustrated in FIG. 5, data broadcast signals are transmitted in order of a data set (A1) and a data set (A2). Until the data set (A1) is updated to the data set (A2), a data set (A1′) and a data set (A1″) having the same content are repeatedly and sequentially transmitted.
Nevertheless, in an HD radio receiver in the past, the time for permitting data reception processing (reception time) and the time for inhibiting data reception processing (reception holding time) are fixedly defined, and the reception time and the reception holding time are alternately switched. This causes unnecessary reception processing in which the repeatedly transmitted data sets (A1′, A1″) having the same content are received during a period when the content of the data set (A1) has not been updated as illustrated in FIG. 5. During the transmission of the data set (A2) updated from the data set (A1), the reception holding time may start. In this case, the updated data set (A2) may not be completely received and may be dropped.
On the other hand, RDS (Radio Data System) broadcast which is practically used mainly in European countries, GAP data describing the transmission intervals of road traffic information is transmitted. This allows switching between road traffic information reception processing and other processing on the basis of the transmission intervals described by the GAP data. For example, there has been proposed a technology that changes the operating period of reception status check on an alternative frequency which is to be performed as the other processing on the basis of the GAP data. (Refer to Japanese Unexamined Patent Application Publication No. 2005-159868).
The road traffic information is transmitted from a road traffic information center through a roadside beacon. It is known that the road traffic information transmitted from the center is updated substantially periodically (about every five minutes). A technology has been proposed which supplies and terminates the power supply to receiving means for receiving the road traffic information in accordance with the update period to prevent unnecessary power consumption during a period when the road traffic information has not been updated. (Refer to Japanese Unexamined Patent Application Publication No. 2008-109572).
However, in HD radio, the number of times of repeated transmission of data sets having the same content is different in accordance with the amount of data to be transmitted in reality. In addition, in HD radio, information describing the number of times of repetition and/or the next timing for updating the content are not transmitted at all. The timing when the content of data sets to be transmitted is updated is not available to HD radio receivers. Thus, the technologies described in Japanese Unexamined Patent Application Publication Nos. 2005-159868 and 2008-109572 may not applicable to HD radio due to the above deficiencies.